Neural circuit for itch and pain.

The somatosensory system is a complex system that responds to changes to the surface or internal state of the body, giving rise to the perceptions of touch, pain, itch and temperature. Stimuli are initially detected at the organs such as skin, and this information is transmitted to the spinal cord. Spinal microcircuits modulate and integrate those signals and this information is transmitted to the brain via spinal projection neurons. However, the neural circuits through which spinal cord neurons encode and discriminate pain, itch, touch and temperature are almost completely unknown. Itch, in particular, is an aversive sensation that can ruin a patient’s quality of life, and for which there are no good treatments. Therefore, the long-term goal of my research is to address how somatosensory inputs are integrated and processed in the spinal cord, with a particular focus on itch.

To tackle the question how spinal microcircuits modulate somatosensory input, I developed a novel electrophysiological technique which allows us, for the first time, to record neural activity of a specific population of spinal cord neurons that are labeled with fluorescent marker while we are applying natural stimulation onto the skin (Hachisuka et al., 2016). Thus, I am now poised to address questions about spinal circuitry that were previously elusive.

Using this new method, I am trying answer following questions: (1) how itch and pain are encoded in the spinal projection neurons; (2) how itch and pain signal are modulated by the spinal interneurons.